JPS649665B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an apparatus for detecting a desired information track on a carrier having adjacent information tracks, comprising:
a transducer for converting information on said information track into electrical form; and a deviation of said transducer from an information track to read the position of said transducer relative to said carrier in a direction transverse to said information track. The present invention relates to an information track detection device having a control means for controlling the information to a minimum. Examples of such sensing devices are inter alia U.S. Pat. No. 3,854,015, U.S. Pat.
Technik” 15-12-1978, page 2, these known examples relate in particular to devices for recording information as optically readable codes on rotating disks. Such devices usually use transducers. The linear motor allows movement along the disc, while the movable mirror keeps the light spot scanning the disc precisely aligned with the desired track on the disc. While the mirror can be considered a coarse control means for coarsely controlling the position of the transducer relative to the carrier, the mirror can be considered a fine control means for finely controlling the position of the transducer relative to the carrier.

In general, the above fine control by mirrors is not necessary in the case of "compact disks".

The invention addresses the problem of rapidly detecting a desired track on an information carrier, in particular a rotating disk provided with an optically readable code. Such disks are referred to in the said publication as "VLP" (wherein, for example, a single circular track on the disk contains a complete television image of one section) and "compact disk" (which generally contains a large number of short pieces of music). (contains a program or audio information with a performance time of several minutes separated by short pauses).

Particularly in the latter case, the detection of particular syllables of audio information is problematic, since in practice a short interruption between two information units represents a reasonable number of adjacent tracks (eg 10-20). This means that when the spacing between tracks is 1-2 μm, there is only a small gap between the end of one information unit and the beginning of the next, and the transducer can be used to separate information units by mechanical means only. This means that it is practically impossible to set it correctly at the starting point.

Although the above-mentioned problem is particularly noticeable in the case of "compact discs," similar problems occur in "VLP" systems when detecting individual film frames separated by short interruptions. Such problems also arise if the signal is not stored in the form of an optically readable code, but in the form of a magnetic code, for example on an information carrier such as a magnetic tape or disk.

The object of the present invention is to provide a solution to the above-mentioned problem not only for "compact disks" but also for "VLP" and for distributing magnetically readable information, for example as will become clear from the following. It also provides a solution for the established carrier.

Therefore, the information track detection device of the present invention supplies a starting pulse to the control means to move the transducer in a direction transverse to the information track with respect to the track, and to move the transducer relative to the track in a direction transverse to the information track. activating pulse supply means for generating an alternating signal for controlling the control means having a frequency dependent on speed; and activating in response to the passing of the zero point of the alternating signal;
timing means for generating a timing signal indicative of a predetermined time after the zero crossing point; and responsive to the timing signal and the alternating signal, a constant track traverse speed of the transducer to the information track is obtained. a control signal supply means for supplying a control signal to the control means indicating a time difference between a point after the predetermined time and a next zero point passing point of the alternating signal, and immediately before reaching the desired information track; braking pulse supply means for supplying a braking pulse to said control means to lock said transducer on said desired information track;
It is characterized by having the following.

The invention is based on the following considerations. By applying an activation pulse, the transducer is moved laterally relative to the information carrier. These small start and stop pulses are provided to cause the transducer to jump from one track to the next, or jump up to one or two tracks before applying braking and then reactivating the controller. It is known per se to cancel deviations between the arrived transducer position and the track position.

However, as mentioned above, a large number of
If it is necessary to jump over a number of tracks between 100 and 100, the information carrier has already traveled a certain distance relative to the transducer before the transducer reaches the desired new track (“VLP ” and “Compact Disc”, the disk rotates by a specific angle).

The distance between tracks is not exactly constant;
In addition, since the track does not extend exactly perpendicular to the movement of the transducer (in the above case, the track is not exactly spiral with a constant pitch, and is eccentric to the center of rotation of the disk). However, in order to suppress the positional deviation between the transducer and the track to be detected, the control loop constituted by the control device must have a large control range, which is not practical.

In the present invention, the requirements placed on the control loop after generation of the stop pulse are less stringent than in conventional tracking because the transducer passes each track at a constant relative velocity or constant cross-track velocity.

A practically advantageous embodiment of the invention is characterized in that a timing circuit measures the time between two zero crossings of the alternating signal and controls the reset time of the monostable multivibrator from this measured value. do.

In this embodiment, the time required to move the transducer one track distance is measured at the time of the activation pulse, and this time is then used as a reference for other control processes. This provides automatic adaptation to changes in eccentricity and/or track distance, resulting in smooth operation of the control system.

The invention will be explained with reference to the drawings.

In FIG. 1, the number 1 indicates a disc-shaped carrier on which optically readable information is placed. Examples of such carriers are known under the names "VLP" (for pulse frequency modulated video information) and "compact disk" (for digitized audio information). The carrier 1 is rotated by a motor 2 so that the information tracks on the carrier pass an optical transducer for reading said information. Examples of such transducers are described in detail in US Pat. No. 4,037,252 and in the references cited above. They are all based on the same method, i.e. the carrier 1 is scanned by a light source 3 and the photodetectors 4, 5, 6 detect an electrical signal (by the detector 4) corresponding to the information on the carrier 1, an information track. An electrical signal (by the detector 5) corresponding to the deviation of the scanning spot relative to the information track in one direction and an electrical signal (by the detector 6) corresponding to the deviation of the scanning spot relative to the information track in the other direction is generated.

The output of the detector 4 is a high-frequency signal hf, the amplitude of which is at a maximum when the scanning spot exactly coincides with the track to be scanned (instant t ₁ in FIG. 2a), but when two scanning tracks In the middle, it decreases to zero. The output terminals of detectors 5 and 6 are connected in push-pull configuration (illustrated by push-pull amplifier 7), which push-pull detector
A control voltage re of the waveform shown in the figure is generated, which passes through zero both at t ₁ when the scanning spot is in the correct position relative to the track and when the scanning spot is exactly halfway between the two tracks. .

This control voltage is applied to a control device such as a linear motor 8.
is supplied in the usual manner and the optical transducer is moved laterally with respect to the carrier 1 by means of a control device.

FIG. 3 shows a circuit diagram of an example of a control circuit provided between the output terminals of the push-pull detectors 5, 6, 7 (control voltage re generation points) and the control device 8 in FIG. The command to start searching for a new information track is supplied by the pulse source 11. The start command can be given manually or derived from information on the carrier 1. The starting pulse from pulse source 11 is sent to two flip-flops 12 and 13.
trigger. Flip-flop 12 connects the control voltage re generation point and control device 8 in FIG.
The original control loop is interrupted between As a result, the optical transducer can be freely moved laterally with respect to the carrier 1. The first displacement is activated by a pulse at point a obtained in the manner described below.

The alternating signal re obtained in FIG. 1 (FIG. 2b) is supplied to a clipper 15, which converts said alternating signal (FIG. 2b) into a square wave signal as shown in FIG. 2c. Since the information tracks on the carrier 1 are not exactly parallel and may exhibit some degree of eccentricity with respect to the axis of rotation of the motor 2, the pulse durations and pulse intervals in FIG. 2c are not equal. Therefore, if switch 14 were to be closed again at any instant, the requirements placed on control loop re-8 to lock onto the new desired track would be transiently severe.

The edges of the square wave voltage in FIG. 2c are differentiated in the differentiating circuit 16 (FIG. 2d), and the resulting (positive) pulses are used to control the monostable multivibrator 1.
Trigger 7. Initially, the monostable multivibrator 17 is inhibited by the output voltage of the flip-flop 13, but after the flip-flop 13 is reset by the output pulse of the differentiator circuit 16, the monostable multivibrator 17 is triggered. Therefore, the monostable multivibrator 17
The square wave voltage shown in figure e is delivered, the leading edge of this square wave corresponds to the pulse of one (positive) sign of the pulse train of figure 2d, and the length (duration) of the square wave pulse is constant, i.e. It is determined by the reset time of the monostable multivibrator 17. After this square wave voltage (Fig. 2e) is inverted in the inverter 19, it is combined with the output voltage of the clipper 15 (Fig. 2c).
Supply acceleration pulse (output a) to AND gate 18
This acceleration pulse can be used to accelerate the optical transducer in a desired direction via the control device 8, while the output voltage of the clipper 15 is inverted in the inverter 20 and then output to the output voltage of the monostable multivibrator 17. with inverted output voltage
A deceleration pulse (output d) is supplied to the AND gate 21 and the control device 8 via the OR gate 22. The waveform in Figure 2g is the AND gate 21
shows the output of (The function of the intermediate OR gate 22 will be explained in detail later). Normally, the output voltages a and d are combined to form the control signal shown in Figure 2h,
It is supplied to the control device 8. Outputs a and d can be combined into one input, for example by using a tri-state logic device.

The operation of the flip-flop 13, which temporarily disables the monostable multivibrator 17, is
This will be explained next with reference to figure f.

At the moment when the activation pulse from the pulse source 11 has deactivated the control loop re-8 via the flip-flop 12 and the switch 14, the optical transducer is free to move relative to the information carrier 1. First, due to the eccentricity of the information tracks, which in practice is several tens of times the spacing between the two tracks, the detectors 5, 6, 7 generate an alternating voltage re, which the optical transducer detects on the track. corresponds to the voltage obtained when moving horizontally from side to side. In that case, the clipper 15 delivers the voltage of FIG. 2c, but since the monostable multivibrator 17 is initially kept inactive by the output voltage of the flip-flop 13, the AND gate 18 is initially in the open state, i.e., as shown in FIG. 2f. The acceleration pulse shown at time t ₁ to _{t 2} is sent out. Differentiator circuit 16 at instant _t2
supplies a reset pulse to flip-flop 13, so that monostable multivibrator 17 becomes triggerable. The monostable multivibrator 17 is therefore only triggered at the instant t ₃ when the differentiating circuit 16 again sends out a positive pulse. After that, the square wave voltage from the monostable multivibrator 17 (second
An acceleration pulse (Fig. 2f) or a deceleration pulse (Fig. 2g) is applied to the control device 8 from the trailing edge of the square wave voltage from the clipper 15 (Fig. 2c).
The acceleration or deceleration pulses, which are derived via AND gates 18 and 21, respectively, cause the optical transducer to have a constant relative velocity with respect to the information track on the carrier 1, ie a constant track traversal velocity.

FIG. 4 shows an embodiment that is a modification of the embodiment shown in FIG. 3. From the alternating signal re (FIG. 2b), the clipper 15 again derives the square wave voltage shown in FIG. 2c, and its edges generate the pulse train shown in FIG. 2d via the differentiating circuit 16. The starting pulse from the pulse source 11 is supplied to the flip-flop 12, which causes the switch 14 to disable the control loop re-8 as well as to disable the OR gate 2.
5 and a timing circuit 26, and the timing circuit 26 is supplied with the output voltage of the clipper 15. This timing circuit is in effect a flip-flop connected to a counter controlled by a clock pulse T, which counter at the instant t ₁ (second
(Fig.) and stops at instant t ₂ . This starting and stopping can be performed by output pulses from the pulse source 11 and the clipper 15, respectively, as shown in the figure.

If desired, stopping can also be effected by a negative output pulse of the differentiator circuit 16. Square wave voltage at the output terminal of the clipper 15 (Fig. 2c)
The measurement value provided by the timing circuit 26, which measures the duration t ₁ -t ₂ of the first pulse of , controls the reset time of the monostable multivibrator 17 . This measured value can be generated in the form of a measured voltage, in which case this measured value is supplied as a bias voltage to the RC circuit of the monostable multivibrator 17, which determines the reset time of this monostable multivibrator. Said time measurements may also be made available in the form of counts, which counts can be stored in memory and which can be reset by the same or another counter generating such counts. Stable multivibrator 1
7 reset time. Furthermore, analysis has shown that the time interval _t1 - _t2 needs to be twice the time interval _t3 - _t4 . This is e.g. a time interval
This can be achieved by a counter that counts up from zero with clock pulses T during t ₁ -t ₂ and then counts down with twice the clock frequency to the count value determined during time interval t ₃ -t ₄ . Therefore, the reset period t ₃ of the monostable multivibrator 17 ~
t ₄ is the period t ₁ measured by the timing circuit 26
~t will be exactly equal to half of ₂ . Therefore, the period t ₃ ~
_t4 is stored in memory by accumulating the maximum count value and thus constitutes the reference for controlling the optical transducer for subsequent track transitions.

The outputs of the clipper 15 and the monostable multivibrator 17 are fed to a gate circuit 18-22 similar to that described above with respect to FIG.
An AND gate 27 is provided between 22 and 22. Note that in order to obtain correct operation of the illustrated circuit, it is necessary to provide a circuit for temporarily exchanging the outputs of the circuit elements 17 and 27 at the beginning of each operation, but this is omitted to simplify the drawing. It has been done.

The operation of this example is as follows. The monostable multivibrator 17 is triggered at the instant the starting pulse is generated from the pulse source 11, and the AND gate 18
(AND gate 21 in the initial stage) is the output terminal a
An acceleration pulse is supplied to the control device 8 via. At the same time, the timing circuit 26 is activated, and the timing circuit 26 outputs the first output voltage of the clipper 15.
The pulse duration t ₁ -t ₂ (Figure 2c) is measured.
When the instant t ₂ is reached, the timing circuit 26 delivers a measured voltage or count value that determines the reset time of the monostable multivibrator 17. At the same time, the timing circuit 26 energizes the AND gate 27, so that the output voltage of the clipper 15 can freely reach the gate circuit 18-22, and then the output voltage shown in FIG. 2c (output of the clipper 15) and 2e
A similar comparison operation for the duration of the diagram (output of the monostable multivibrator 17) is performed as described above with respect to FIG. The advantage of making the reset time of the monostable multivibrator 17 dependent on the duration of the first acceleration pulse at output terminal a is that
Adaptability to the eccentricity of the information carrier 1 and the distance between the tracks of this carrier, which varies within certain limit values, is achieved, so that the control system does not react abruptly or abruptly. Furthermore, if it is necessary to compare the above-mentioned durations each time the voltage re (FIG. 2b) passes through the zero point, a polarity inversion switch is provided in the differentiating circuit 16 and the AND gates 18 and 22, and the voltage re (FIG. 2b) is Figure 2b) The sign of the output pulse is inverted each time the polarity changes.

The means necessary to stop the control device 8 when the desired track is reached are shown in the lower half of FIGS. 3 and 4, respectively. Such means comprise a counter 31 which is set to a count value (shown diagrammatically by a switch 32) corresponding to the desired number of tracks to be skipped, and whose input terminal is connected to a differentiating circuit 16.
Since it is connected to the output terminal of (in the case of Figure 3)
A down count is performed each time a track is passed. When the count value of the counter 31 becomes zero, the output terminal d
It is necessary to generate a braking pulse at
4 needs to be switched on again.

In practice, the braking pulse is approximately 1/4 of the waveform in Figure 2b from the zero point passing time corresponding to the new desired track.
Preferably, it starts earlier than the cycle. For this purpose, the output signals re of the detectors 5, 6, 7 (Fig. 2b) are supplied to a differentiating circuit 33 so as to obtain the voltage waveform of Fig. 2i. This voltage is the clipper 3
4 to flip-flop 35.

The operation of the flip-flop 35 is controlled by the counter 31.
is prohibited by the counter 31 unless the count value has reached zero. When the counter 31 reaches a count value of zero, the flip-flop 35 is switched to its state at the next zero-crossing instant t _x of the waveform of FIG. 2i. This instant is 1/4 period before the instant (instant t _y ) at which the waveform in FIG. 2b passes through the zero point. The output of flip-flop 35 is supplied to OR gate 22, whose output d supplies a braking pulse of duration t _x -t _y to control device 8. At the instant _ty , the flip-flop 35 is reset and generates a reset pulse for the flip-flop 12 via the differentiating circuit 36, so that the switch 14 is switched on again and the control loop re-8 is activated again.

It is clear that the invention is equally applicable to both "compact disks" and "VLPs". It can also be applied to magnetic disk storage devices, in which case magnetic transducers are used. In "compact disks", the motor for moving the optical transducer relative to the information carrier is generally not a linear motor, but the optical transducer is arranged on a pivoting arm, so that the movement of the optical transducer is no longer possible. It is no longer pure linearity.

The switches shown in Figures 3 and 4 are usually electronic, for example of the MOS type.

Clipper or monostable multivibrator 17
A changeover switch may be provided in the connection between the gate circuits 18 and 18-22 to enable switching between acceleration and deceleration pulses depending on the direction of movement of the transducer.

[Brief explanation of drawings]

1 is a schematic diagram showing a known tracking device for optically encoded information carriers; FIG. 2 is an illustration of the operation of FIG. 1 and an embodiment of the invention; and FIG. 3 is an embodiment of the invention. Block Diagram FIG. 4 is a block diagram showing a modified embodiment of FIG. 3. 1...Carrier, 2...Motor, 3...Light source, 4, 5, 6
...Photodetector, 7...Push-pull amplifier, 8...Control device, 11...Pulse source, 12, 13...Flip-flop, 15...Clipper, 16...Differentiating circuit, 17
...monostable multivibrator, 26...timing circuit, 31...counter, 33...differentiator circuit, 34...
Clipper, 35... flip-flop, 36... differential circuit.

Claims (1)

Claims: 1. A device for detecting a desired information track on a carrier having adjacent information tracks, comprising: a transducer for converting information on the information track into electrical form; and a transducer for converting the information on the information track into electrical form; an information track sensing device comprising: control means for controlling the position of the transducer relative to the carrier in a direction transverse to the track so as to minimize the deviation of the transducer from the information track to be read; providing an activation pulse to the control means to move the transducer in a direction across the information track relative to the track, the trigger pulse having a frequency dependent on the relative transversal velocity of the transducer with respect to the track; a starting pulse supply means for generating an alternating signal for controlling the control means; and a starting pulse supply means for starting in response to the passing of the zero point of the alternating signal, and generating a timing signal indicating a time point after a predetermined time from the point of passing the zero point. timing means, responsive to said timing signal and said alternating signal, for determining a time point after said predetermined time and the next zero of said alternating signal so as to obtain a constant cross-track velocity of said transducer with respect to said information track; control signal supply means for supplying a control signal to said control means indicative of a time difference between said transducer and said transducer; An information track detection device comprising: braking pulse supply means for locking the information track on the information track. 2. A monostable multivibrator is used as the timing means, while a gate circuit is used as the control signal supply means, and the monostable multivibrator is activated when the alternating signal passes a zero point after the activation pulse is generated. , the output pulse of the monostable multivibrator is transferred as the timing signal to the gate circuit, and the gate circuit has a duration determined by the time difference between the point after the predetermined time and the next zero point crossing point of the alternating signal. 2. The information track detection device according to claim 1, wherein the information track detection device generates an output having the following value as the control signal. 3. It further comprises a timing circuit for measuring the time between two zero-point passing points of the alternating signal, and means for obtaining a control amount for controlling the reset time of the monostable multivibrator from this measured value. An information track detection device according to claim 2, characterized in that: 4. Information track detection according to claim 3, wherein the control amount corresponds to the reset time of the monostable multivibrator and is half the time measured by the timing circuit. Device. 5. Claims further comprising means for counting the number of information tracks that have passed, wherein the braking pulse supply means generates the braking pulse after the counting means has counted a predetermined number of information tracks. The information track detection device according to any one of items 1 to 4.